1. Field of Invention
Embodiments of the invention are related to evaluation of subsurface reservoirs.
2. Description of Related Art
In the oil and gas industry, geologic models are often used to aid in activities, such as determining the locations of wells, estimating hydrocarbon reserves, or planning reservoir-development strategies, including evaluating the economic recovery of hydrocarbon resources. A geologic model typically is a computer-based representation of a subsurface earth volume, such as a petroleum reservoir or a depositional basin.
Geologic models may take on many different forms. Depending on the context, descriptive or static geologic models built for petroleum applications can be in the form of a 3-D array of cells, to which geologic and/or geophysical properties such as lithology, porosity, acoustic impedance, permeability, or water saturation are assigned (such properties will be referred to collectively herein as “reservoir properties”).
Many geologic models are constrained by stratigraphic or structural surfaces (e.g., flooding surfaces, sequence interfaces, fluid contacts, faults) and boundaries (e.g., facies changes). These surfaces and boundaries define regions within the model that possibly have different reservoir properties.
Various approaches can be followed for evaluating a reservoir using geologic modeling. At least one approach is strictly sequential, involving sequential evaluations by several disciplines. With such an approach, a reservoir evaluation using geologic modeling might take several or many months to complete. With such an approach, due to the large amount of time necessary for evaluating a reservoir using geologic modeling, only one geologic model would tend to be built in connection with the reservoir evaluation. Consequently, such an approach would allow no realistic opportunity to learn how decisions are made during the geologic modeling process, or how such decisions would affect the final outcome. Such a strict sequential approach would also allow no opportunity to evaluate the inherent uncertainty in arriving at solutions to problems, considering the limited amount of data that would tend to be available for use in the geologic modeling as well as the level of interpretation required in the geologic modeling process.
Furthermore, such a strict sequential approach for evaluating a reservoir using geologic modeling would in all likelihood tend to involve building a geologic model made up of many millions of cells, e.g., 200 million cells, and require “upscaling” the geologic model in order to reduce the number of cells to no more than 500,000 cells so that flow simulation could be performed. Obviously, the steps of building geologic models and then upscaling them would tend to contribute further to the large amount of time needed to evaluate a reservoir using geologic modeling.
Accordingly, a need exists for improved methods of evaluating reservoir.